Abstract by Ka-Hei Law
In star forming galaxies, dust plays a significant role in shaping the ultraviolet (UV) through infrared (IR) spectrum. Dust attenuates the radiation from stars, and re-radiates the energy through equilibrium and non-equilibrium emission. Polycyclic aromatic hydrocarbons (PAH), graphite, and silicates contribute to different features in the spectral energy distribution; however, they are all highly opaque in the same spectral region - the UV. Compared to old stellar populations, young populations release a higher fraction of their total luminosity in the UV, making them a good source of the energetic UV photons that can power dust emission. However, given their relative abundance, the question of whether young or old stellar populations provide most of these photons that power the infrared emission is an interesting question. Using three samples of galaxies observed with the Spitzer Space Telescope and our dusty radiative transfer model, we find that young stellar populations (on the order of 100 million years old) dominate the dust heating in star forming galaxies, and old stellar populations (13 billion years old) generally contribute less than 20% of the far-IR luminosity.
Relevant Papers
"Young, UV-bright Stars Dominate Dust Heating in Star Forming Galaxies"
Law et al. 2011
Talk Slides
pdf
Friday, August 19, 2011
Friday, August 5, 2011
Star formation in 30 Doradus
Abstract by De Marchi et al.
Using observations obtained with the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope (HST), we have studied the properties of the stellar populations in the central regions of 30 Dor, in the Large Magellanic Cloud. The observations clearly reveal the presence of considerable differential extinction across the field. We characterise and quantify this effect using young massive main sequence stars to derive a statistical reddening correction for most objects in the field. We then search for pre-main sequence (PMS) stars by looking for objects with a strong (> 4 sigma) Halpha excess emission and find about 1150 of them over the entire field. Comparison of their location in the Hertzsprung-Russell diagram with theoretical PMS evolutionary tracks for the appropriate metallicity reveals that about one third of these objects are younger than ~4Myr, compatible with the age of the massive stars in the central ionising cluster R136, whereas the rest have ages up to ~30Myr, with a median age of ~12Myr. This indicates that star formation has proceeded over an extended period of time, although we cannot discriminate between an extended episode and a series of short and frequent bursts that are not resolved in time. While the younger PMS population preferentially occupies the central regions of the cluster, older PMS objects are more uniformly distributed across the field and are remarkably few at the very centre of the cluster. We attribute this latter effect to photoevaporation of the older circumstellar discs caused by the massive ionising members of R136.
Relevant Papers
"Star formation in 30 Doradus"
De Marchi et al.
Talk Slides
pdf
Using observations obtained with the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope (HST), we have studied the properties of the stellar populations in the central regions of 30 Dor, in the Large Magellanic Cloud. The observations clearly reveal the presence of considerable differential extinction across the field. We characterise and quantify this effect using young massive main sequence stars to derive a statistical reddening correction for most objects in the field. We then search for pre-main sequence (PMS) stars by looking for objects with a strong (> 4 sigma) Halpha excess emission and find about 1150 of them over the entire field. Comparison of their location in the Hertzsprung-Russell diagram with theoretical PMS evolutionary tracks for the appropriate metallicity reveals that about one third of these objects are younger than ~4Myr, compatible with the age of the massive stars in the central ionising cluster R136, whereas the rest have ages up to ~30Myr, with a median age of ~12Myr. This indicates that star formation has proceeded over an extended period of time, although we cannot discriminate between an extended episode and a series of short and frequent bursts that are not resolved in time. While the younger PMS population preferentially occupies the central regions of the cluster, older PMS objects are more uniformly distributed across the field and are remarkably few at the very centre of the cluster. We attribute this latter effect to photoevaporation of the older circumstellar discs caused by the massive ionising members of R136.
Relevant Papers
"Star formation in 30 Doradus"
De Marchi et al.
Talk Slides
Friday, July 22, 2011
Highlights of Four Decades of Research on Massive Stars: A Scientific Meeting in the Honour of Anthony F.J. Moffat
Abstract
We are organizing a meeting to celebrate four decades of contributions of Professor Anthony F.J. Moffat to massive-star research. Since his first papers on open clusters in the early 70’s, Tony’s research interests have expanded in many directions to cover a multitude of aspects of massive stars. The meeting will encompass the following main subjects on which he has worked during his career:
* Young open star clusters: keys to understanding massive stars
* Galactic structure and dynamics; runaway stars
* Massive binaries: orbits, masses, mass-loss rates, binary frequency, colliding winds, dust formation
* The most massive stars
* The true nature of clumping in hot stellar winds and its consequences
* Rotation and magnetic fields
* Pulsations (e.g. MOST and soon BRITE-Constellation)
* WR surveys (Galactic and extra-galactic)
Talk Slides
pdf
We are organizing a meeting to celebrate four decades of contributions of Professor Anthony F.J. Moffat to massive-star research. Since his first papers on open clusters in the early 70’s, Tony’s research interests have expanded in many directions to cover a multitude of aspects of massive stars. The meeting will encompass the following main subjects on which he has worked during his career:
* Young open star clusters: keys to understanding massive stars
* Galactic structure and dynamics; runaway stars
* Massive binaries: orbits, masses, mass-loss rates, binary frequency, colliding winds, dust formation
* The most massive stars
* The true nature of clumping in hot stellar winds and its consequences
* Rotation and magnetic fields
* Pulsations (e.g. MOST and soon BRITE-Constellation)
* WR surveys (Galactic and extra-galactic)
Talk Slides
Friday, July 8, 2011
The Most Massive Stars in the Universe
Abstract by Jorick Vink
The recent detection of a gamma-ray burst just a few hundred millions years after the Big Bang provides strong evidence that massive stars can form and die when the Universe was not yet enriched. Recent studies also reveal the existence and deaths of stars up to 300 solar masses in our local Universe. Might such objects produce superluminous supernovae, or even pair-instability supernovae? Do they suffer extreme mass loss ending their lives as "normal" Wolf-Rayet stars instead? Could they explode prematurely as Luminous Blue Variables? In order to address these issues, I discuss the latest developments in mass loss and evolution modelling - as a function of host galaxy metallicity.
Relevant Papers
"Wind modelling of very massive stars up to 300 solar masses"
Vink et al. 2011
"The VLT-FLAMES Tarantula Survey. III. A very massive star in apparent isolation from the massive cluster R136"
Bestenlehner et al. 2011
Talk Slides
pdf
The recent detection of a gamma-ray burst just a few hundred millions years after the Big Bang provides strong evidence that massive stars can form and die when the Universe was not yet enriched. Recent studies also reveal the existence and deaths of stars up to 300 solar masses in our local Universe. Might such objects produce superluminous supernovae, or even pair-instability supernovae? Do they suffer extreme mass loss ending their lives as "normal" Wolf-Rayet stars instead? Could they explode prematurely as Luminous Blue Variables? In order to address these issues, I discuss the latest developments in mass loss and evolution modelling - as a function of host galaxy metallicity.
Relevant Papers
"Wind modelling of very massive stars up to 300 solar masses"
Vink et al. 2011
"The VLT-FLAMES Tarantula Survey. III. A very massive star in apparent isolation from the massive cluster R136"
Bestenlehner et al. 2011
Talk Slides
Friday, June 10, 2011
Observations of Boron in Rapidly Rotating Early-B Stars
Abstract by Charles Proffitt
We discuss new HST/STIS observations of the B III resonance doublet in 26 early-B stars with projected rotational velocities between 50 and 220 km/s and compare the measured boron abundances with predictions of stellar evolution models that include rotationally induced mixing. Our results suggest that some stars show significantly less mixing than predicted by the models. When combined with previous results for stars with low projected rotational velocities (below 50 km/s) the distribution of [B/H] with V sin(i) bears a strong resemblance to that for nitrogen, the so-called Hunter diagram (Hunter et al 2008). Especially surprising is the apparent detection of substantial boron in two Be stars that are believed to be very rapid rotators viewed at small inclination angles for which the true rotational velocities are at 75 - 80% of the breakup limit.
Relevant Papers
"Testing Rotational Mixing Predictions with New Boron Abundances in Main-Sequence B-Type Stars"
Mendel et al 2006
"Nitrogen enrichment, boron depletion and magnetic fields in slowly-rotating B-type dwarfs"
Morel et al 2008
"Rotating Massive Main-Sequence Stars I: Grids of Evolutionary Models and Isochrones"
Bortt et al. 2011a
"Rotating Massive Main-Sequence Stars II: Simulating a Population of LMC early B-type Stars as a Test of Rotational Mixing"
Brott et al. 2011b
Talk Slides
pdf
We discuss new HST/STIS observations of the B III resonance doublet in 26 early-B stars with projected rotational velocities between 50 and 220 km/s and compare the measured boron abundances with predictions of stellar evolution models that include rotationally induced mixing. Our results suggest that some stars show significantly less mixing than predicted by the models. When combined with previous results for stars with low projected rotational velocities (below 50 km/s) the distribution of [B/H] with V sin(i) bears a strong resemblance to that for nitrogen, the so-called Hunter diagram (Hunter et al 2008). Especially surprising is the apparent detection of substantial boron in two Be stars that are believed to be very rapid rotators viewed at small inclination angles for which the true rotational velocities are at 75 - 80% of the breakup limit.
Relevant Papers
"Testing Rotational Mixing Predictions with New Boron Abundances in Main-Sequence B-Type Stars"
Mendel et al 2006
"Nitrogen enrichment, boron depletion and magnetic fields in slowly-rotating B-type dwarfs"
Morel et al 2008
"Rotating Massive Main-Sequence Stars I: Grids of Evolutionary Models and Isochrones"
Bortt et al. 2011a
"Rotating Massive Main-Sequence Stars II: Simulating a Population of LMC early B-type Stars as a Test of Rotational Mixing"
Brott et al. 2011b
Talk Slides
Friday, May 27, 2011
Young Stellar Objects in the Magellanic Clouds: Identification based on the Spitzer and Herschel Observations
Abstract by Marta Sewilo
The Surveying the Agents of a Galaxy's Evolution (SAGE) Spitzer Legacy Programs provide a comprehensive picture of the current star formation activity in the Large (SAGE-LMC, Meixner et al. 2006) and Small (SAGE-SMC, Gordon et al. 2011) Magellanic Clouds which is traced by the IRAC (3.6, 4.5, 5.8, and 8.0 microns) and MIPS (24, 70, and 160 microns) bands. It allowed for the first time a global study of star formation in the Magellanic Clouds (MCs) at high enough resolution to resolve individual cores and protostars at a range of mid-IR wavelengths. The methods for searching and identifying Young Stellar Objects (YSOs) in the MCs will be discussed. These methods involve color-magnitude selections, inspection of the multi-wavelength images, and fitting of the spectral energy distributions of the YSO candidates using the 2D radiative transfer models (Robitaille et al. 2006).
The most recent data from the "HERschel Inventory of the Agents of Galaxy Evolution” (HERITAGE; Meixner et al. 2010) survey provided reliable longwave (100 - 500 microns) SEDs of large samples of Spitzer-identified high-mass YSOs, thus constraining their physical properties and evolutionary stages more precisely than was previously possible. Herschel also discovers the youngest YSOs whose SEDs peak in Herschel bands.
Relevant Papers
"Spitzer Sage Survey of the Large Magellanic Cloud. III. Star Formation and ~1000 New Candidate Young Stellar Objects"
Whitney et al. 2008
"High- and Intermediate-Mass Young Stellar Objects in the Large Magellanic Cloud"
Gruendl and Chu 2009
"The youngest massive protostars in the Large Magellanic Cloud"
Sewilo et al. 2010
Talk Slides
pdf
The Surveying the Agents of a Galaxy's Evolution (SAGE) Spitzer Legacy Programs provide a comprehensive picture of the current star formation activity in the Large (SAGE-LMC, Meixner et al. 2006) and Small (SAGE-SMC, Gordon et al. 2011) Magellanic Clouds which is traced by the IRAC (3.6, 4.5, 5.8, and 8.0 microns) and MIPS (24, 70, and 160 microns) bands. It allowed for the first time a global study of star formation in the Magellanic Clouds (MCs) at high enough resolution to resolve individual cores and protostars at a range of mid-IR wavelengths. The methods for searching and identifying Young Stellar Objects (YSOs) in the MCs will be discussed. These methods involve color-magnitude selections, inspection of the multi-wavelength images, and fitting of the spectral energy distributions of the YSO candidates using the 2D radiative transfer models (Robitaille et al. 2006).
The most recent data from the "HERschel Inventory of the Agents of Galaxy Evolution” (HERITAGE; Meixner et al. 2010) survey provided reliable longwave (100 - 500 microns) SEDs of large samples of Spitzer-identified high-mass YSOs, thus constraining their physical properties and evolutionary stages more precisely than was previously possible. Herschel also discovers the youngest YSOs whose SEDs peak in Herschel bands.
Relevant Papers
"Spitzer Sage Survey of the Large Magellanic Cloud. III. Star Formation and ~1000 New Candidate Young Stellar Objects"
Whitney et al. 2008
"High- and Intermediate-Mass Young Stellar Objects in the Large Magellanic Cloud"
Gruendl and Chu 2009
"The youngest massive protostars in the Large Magellanic Cloud"
Sewilo et al. 2010
Talk Slides
Friday, May 13, 2011
Not Your Grandmother's HII Regions: An X-ray Tour of Massive Star-forming Regions
Abstract by Leisa Townsley
The Chandra X-ray Observatory is providing remarkable new views of massive star-forming regions, revealing all stages in the life cycle of high-mass stars and their effects on their surroundings. We will tour several such regions, highlighting physical processes that characterize the life of a cluster of massive stars, from deeply-embedded cores too young to have established an HII region to superbubbles so large that they shape our views of galaxies. Along the way we see that X-ray observations reveal hundreds of pre-main sequence stars accompanying the massive stars that power great HII region complexes. The most massive stars themselves are often anomalously hard X-ray emitters; this may be a new indicator of close binarity or strong magnetic fields. These complexes are sometimes suffused by diffuse X-ray structures, signatures of multi-million-degree plasmas created by fast O-star winds. In older regions we see the X-ray remains of the deaths of massive stars that stayed close to their birthplaces, exploding as cavity supernovae within the superbubbles that these clusters created.
Relevant Papers
"The Integrated Diffuse X-ray Emission of the Carina Nebula Compared to Other Massive Star-forming Regions", Townsley et al. 2011
Talk Slides
pdf
The Chandra X-ray Observatory is providing remarkable new views of massive star-forming regions, revealing all stages in the life cycle of high-mass stars and their effects on their surroundings. We will tour several such regions, highlighting physical processes that characterize the life of a cluster of massive stars, from deeply-embedded cores too young to have established an HII region to superbubbles so large that they shape our views of galaxies. Along the way we see that X-ray observations reveal hundreds of pre-main sequence stars accompanying the massive stars that power great HII region complexes. The most massive stars themselves are often anomalously hard X-ray emitters; this may be a new indicator of close binarity or strong magnetic fields. These complexes are sometimes suffused by diffuse X-ray structures, signatures of multi-million-degree plasmas created by fast O-star winds. In older regions we see the X-ray remains of the deaths of massive stars that stayed close to their birthplaces, exploding as cavity supernovae within the superbubbles that these clusters created.
 |
| 30 Doradus (Chandra soft X-rays in red, MCELS H-alpha in green, Spitzer 8 microns in blue) |
Relevant Papers
"The Integrated Diffuse X-ray Emission of the Carina Nebula Compared to Other Massive Star-forming Regions", Townsley et al. 2011
Talk Slides
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